The invention generally relates to systems and techniques to actuate isolation valves, such as formation isolation valves, for example.
A formation isolation valve may be used in a well for such purposes as preventing fluid loss and controlling an underbalanced condition. The valve forms a controllable sealed access to formations below the valve. When the valve is open, well equipment (a tubular string, a wireline system, a slickline system, etc.) may be deployed through the valve for purposes of performing one or more testing, perforating and/or completion functions below the valve. After these functions are complete, the well equipment may be retrieved, and the valve may be subsequently closed.
For purposes of opening and closing the valve, an intervention may be performed. In the intervention, a tool, such as a shifting tool, is run downhole into the well to engage and change the state of the valve. After the formation isolation valve is closed, the well may be suspended for days or months.
A well intervention typically consumes a significant amount of time and money. Therefore, interventionless techniques have been developed to operate the formation isolation valve. For example, a conventional formation isolation valve may include a chamber that has precharged nitrogen, which acts as a gas spring for purposes of providing downhole power to operate the valve. More specifically, a control mechanism (a J-slot-based mechanism, for example) of the valve, which limits expansion of the nitrogen is remotely controlled from the surface by manipulating the well pressure. After a given sequence of well pressure fluctuations, the control mechanism allows the nitrogen to expand to push a piston for purposes of rotating a ball valve element of the valve open.
A potential challenge in using the above-described formation isolation valve with precharged nitrogen is that the gas chamber of the valve typically is charged on the rig floor next to rig personnel before the valve is run downhole and installed. In addition, under certain well conditions, the well pressure may exceed the rating of the tools in the well or the rating of the ball valve element during the sequence of pressure fluctuations.
Thus, there exists a continuing need for better ways to remotely actuate a downhole tool, such as a formation isolation valve, for example.